And that's what a new satellite launching tomorrow, dubbed the Orbiting Carbon Observatory (OCO) is designed to find out. "With the launch of OCO, scientists will be able to study CO2 concentration from the surface of the Earth to the top of the atmosphere," says Eric Ianson, OCO science program executive at NASA. "Its high-resolution measurements will provide a more complete picture of human and natural sources of CO2 at the local and regional scale."

Humans have been steadily adding to the total CO2 in the atmosphere by burning fossil fuels—prior to the Industrial Revolution atmospheric concentrations stood at about 280 parts per million (ppm). Now CO2 makes up some 386 ppm in the atmosphere—and is rising rapidly. "On average, there are about four billion metric tons more of carbon in the atmosphere each year," says Anna Michalak, an OCO team scientist at the University of Michigan at Ann Arbor. "This increase in carbon is contributing to climate change."

At present, CO2 is mostly monitored from a series of ground observation stations, the most of famous of which—Mauna Loa Observatory in Hawaii—has been measuring atmospheric CO2 levels since 1958. But even all 100 of these ground stations (plus high-flying aircraft) put together will not match the information provided by just one 16-day orbit of OCO.

The $278-million program will employ three spectrometers to analyze light reflected off Earth. Paired with precise data about where the satellite is—using the same Global Positioning System a cell phone taps, according to Mike Miller, vice president of science and technology programs at satellite-maker Orbital Sciences Corp.—OCO will be able to determine how many CO2; molecules are in that slice of the atmosphere based on how much infrared light has been absorbed.

"No other molecules have dynamics that are the same as these motions [of CO2]. They act as molecular fingerprints," says Charles Miller, OCO deputy principal investigator at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. "Using very accurate measurements of the changes in the amount of light that are being absorbed by CO2, we can make a very precise measurements of the number of CO2 molecules in the atmosphere."

And that will enable scientists to determine what parts of the planet are responsible for pumping out CO2—coal-fired power plants, highways but also decaying forests—or absorbing it. "We'll have much more information on where the CO2 is, and from that we can infer where the sources are and where the sinks are," says David Crisp, OCO principal investigator at JPL.

To make the analysis, the satellite will orbit at an altitude of 438 miles (705 kilometers) traveling some 4.3 miles (seven kilometers) per second. It will take three measurements per second from its polar orbit, which allows it to circle Earth from pole to pole as the planet rotates beneath it, thereby allowing coverage of the whole globe. NASA expects the satellite to perform some eight million such measurements every 16 days, an avalanche of CO2 data that will roll over researchers for at least the next two years.

The Taurus XL rocket that will carry the nearly half-ton satellite much of the way to its orbit, scheduled to blast off at 4:51 A.M. Eastern time on February 24. In orbit it will be part of the "A-Train" of NASA satellites and will help supplement the data gathered by the Japanese Greenhouse Gases Observing Satellite (GOSAT or "Ibuki" to the Japanese), which uses an interferometer to measure levels of both CO2 and methane, another powerful greenhouse gas. For the next few months, scientists will perform instrument checks and validate the data—as well as boost OCO to its operational orbit—before data starts flowing in the fall, according to Ralph Basilio, OCO deputy project manager at JPL.

By identifying the parts of the planet absorbing CO2, scientists hope to be able to predict how they might behave in the future. After all, if the oceans and forests absorb their fill—as seems to be happening in the Southern Ocean—atmospheric concentrations could rise much faster than anticipated in future. "We need to understand why plants and oceans are taking up as much carbon as they are and how this will change in future," Michalak adds. "It is important to be able to predict how things will change in the future."

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